1. Field of the Disclosure
The present disclosure relates to fixing two rotatable parts together. Aspects of the present disclosure relate to fixing two rotatable parts of a gas turbine engine together.
2. Description of the Related Art
An axial-flow gas turbine engine comprises a compressor, a combustor and a turbine. As the flow passes through the compressor, the pressure increases, resulting in a net forward force on the compressor. As the flow passes through the turbine, the pressure decreases, resulting in a net rearward force on the turbine.
A typical compressor comprises multiple stages, each one of which has a set of rotor blades provided at a given axial location. In use, multiple stages of rotor blades typically all rotate at the same axial rate. Furthermore, these rotor blade stages also rotate at the same axial rate as one or more corresponding rotor blade stages of the turbine.
The compressor and turbine are typically joined by a shaft. The shaft transmits power from the turbine to the compressor. Accordingly, the shaft, multiple compressor stages and one or more turbine stages all rotate at the same rate in use.
Turning to the compressor stages, one way of ensuring that each compressor stage rotates at the same rate is to machine the parts of each stage that hold the blades (for example the rotor discs) and their connecting parts from a single metallic block. However, this is expensive, and limits the design freedom as it requires all stages to be manufactured using the same material. This may not be desirable because the different flow conditions (for example in terms of temperature and/or pressure) experienced by each of the stages may mean that different materials are best suited to for the different stages.
If the stages are not to be machined from a single block, then the individual rotor stages must be held together. However, due to the pressure increase through a compressor, there is very significant axial force pushing neighbouring rotor stages axially apart. Thus, it may not be feasible and/or desirable to attach neighbouring rotor stages together using conventional means, particularly for engines that have high pressure rises across the compressor. For example, such conventional means may be required to be unacceptably large and/or heavy.
Similarly, due to the pressure decrease through the turbine, it may not be feasible to attach neighbouring rotor stages of a turbine together using conventional means. Furthermore, it may not be feasible and/or desirable to attach a part of the shaft (that connects the turbine and compressor together) either to another part of the shaft or to a part of the compressor or turbine using conventional means.